Nanomaterial having tunable infrared absorption characteristics and associated method of manufacture

ABSTRACT

A quantum nanomaterial having a bandgap that may be tuned to enable the quantum nanomaterial to detect IR radiation in selected regions including throughout the MWIR region and into the LWIR region is provided. The quantum nanomaterials may include tin telluride (SnTe) nanomaterials and/or lead tin telluride (Pb x Sn 1-x Te) nanomaterials. Additionally, a method of manufacturing nanomaterial that is tunable for detecting IR radiation in selected regions, such as throughout the MWIR region and into the LWIR region, is also provided.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/388,750, filed Oct. 1, 2010, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

Embodiments of the present disclosure relate generally to nanomaterialsand, more particularly, to nanomaterials having tunable infrared (IR)absorption characteristics as well as associated methods for manufactureof such nanomaterials.

BACKGROUND

In a number of applications, it is desirable to be able to detect IRsignals. As such, a variety of IR sensors and coatings have beendeveloped in order to collect and detect IR radiation. Typically, theseIR sensors or coatings are designed to detect IR radiation within aspecific bandwidth, such as within all or a portion of the near-infrared(NIR) bandwidth defined as 0.75-1.4 μm in wavelength, the shortwavelength infrared (SWIR) bandwidth defined as 1.4-3 μm in wavelength,the mid-wavelength infrared (MWIR) bandwidth defined as 3-5 μm inwavelength, or the long-wavelength infrared (LWIR) bandwidth defined as5-15 μm in wavelength.

Some IR detectors are formed of bulk semiconductor materials. The bulksemiconductor materials absorb infrared radiation at their bandgap. Itis desirable in at least some applications to be able to tune the IRdetector so as to detect a particular bandwidth of IR radiation.However, the bandwidth of the IR radiation that is absorbed by the bulksemiconductor materials can only be tuned by changing the composition ofthe semiconductor materials. As such, IR detectors that are formed ofbulk semiconductor materials have typically been utilized to detect theNIR and SWIR bandwidths with few IR detectors formed of bulksemiconductor materials being constructed so as to detect IR radiationin the MWIR and/or LWIR bandwidths. However, IR detectors formed of abulk Hg_(1-x)Cd_(x)Te material have been utilized to detect IR radiationthroughout the MWIR and LWIR regions as a result of its relatively lowbandgap. Unfortunately, Hg_(1-x)Cd_(x)Te has a relatively high toxicitylevel and may be quite expensive, thereby rendering it unsuitable for anumber of applications and, in any event, posing at least somechallenges during its manufacture and scalability.

As an alternative to the use of bulk semiconductor materials for IRdetectors, quantum nanomaterials, such as quantum dots, quantum rods andnano-tetrapods, have been developed that are also capable of absorbingIR radiation. As such, IR detectors may incorporate quantumnanomaterials, i.e., dots, quantum rods or nano-tetrapods, or thesematerials may be incorporated into paints or other coatings such thatthe resulting paints or other coatings are sensitive to and capable ofabsorbing incident IR radiation. Quantum dots, quantum rods andnano-tetrapods have a bandgap that may be tuned by altering the size andmorphology of the quantum dots, quantum rods and nano-tetrapods so as tocorrespondingly alter the region within the IR spectrum to which thequantum nanomaterials are sensitive. However, much of the priordevelopment of nanomaterials such as quantum dots, quantum rods andnano-tetrapods that exhibit quantum confinement has been focused onachieving a relatively high quantum yield (QY) in which the nanomaterialefficiently absorbs and re-emits across the tunable bandgap with thenanomaterial system. Quantum dots, quantum rods and nano-tetrapods aretherefore generally configured to absorb visible light, as well as IRradiation in the NIR and SWIR regions and, in some instances, a portionof the MWIR region, but have not generally been capable of absorbing thelonger wavelength portion of the MWIR region or the LWIR region of IRradiation.

As such, it may be desirable to provide improved techniques fordetecting IR radiation including, for example, improved techniques fordetecting IR radiation throughout the MWIR region and into the LWIRregion.

BRIEF SUMMARY

A quantum nanomaterial having a bandgap that may be tuned to enable thequantum nanomaterial to absorb IR radiation in selected regionsincluding throughout the MWIR region and into the LWIR region isprovided in accordance with one embodiment. Additionally, a method ofmanufacturing nanomaterial that is tunable for absorbing IR radiation inselected regions, such as throughout the MWIR region and into the LWIRregion, is provided according to another embodiment.

A quantum nanomaterial is provided in accordance with one embodimentthat includes at least one tin telluride (SnTe) nanocrystal having across-sectional dimension of between 15 nm and 50 nm. The SnTenanocrystal of this embodiment has a bandgap between 0 eV and 0.35 eVdependent, at least partially, upon the cross-sectional dimensions ofthe SnTe nanocrystal. The SnTe nanocrystal of this embodiment also haspeak absorption for signals having a wavelength of at least 3.5 μm. Inone embodiment, the SnTe nanocrystal has peak absorption for signalshaving a wavelength of at least 4.2 μm and, in a further embodiment, forsignals having a wavelength of at least 8 μm.

A quantum nanomaterial of another embodiment includes at least one leadtin telluride (Pb_(x)Sn_(1-x)Te) nanocrystal in which x is a valuebetween 0.1 and 0.6. The Pb_(x)Sn_(1-x)Te nanocrystal of this embodimenthas a cross-sectional dimension of at least 7.5 nm. The Pb_(x)Sn_(1-x)Tenanocrystal also has a bandgap of between 0 eV and 0.35 eV dependent, atleast partially, upon the cross-sectional dimensions of thePb_(x)Sn_(1-x)Te nanocrystal and/or the value of x. The Pb_(x)Sn_(1-x)Tenanocrystal also has peak absorption for signals having a wavelength ofat least 3.5 μm. In one embodiment, the Pb_(x)Sn_(1-x)Te nanocrystal haspeak absorption for signals having a wavelength of at least 4.4 μm and,in a further embodiment, for signals having a wavelength of at least 8μm.

In accordance with another embodiment, a method of manufacturing a tintelluride (SnTe) nanomaterial comprises mixing a tin (Sn) precursorsolution and a telluride (Te) solution to form a solution. The solutionis then maintained at an elevated temperature for a period of time. Inaccordance with this embodiment, additional amounts of the Sn precursorsolution and the Te solution are repeatedly injected into the solutionat different points in time following the initial mixing of the Snprecursor solution and the Te solution. Further, the solution ismaintained at an elevated temperature for a period of time following thesubsequent injection of an additional amount of the Sn precursorsolution and the Te solution into the solution prior to the subsequentinjection of an additional amount of the Sn precursor solution and theTe solution.

In one embodiment, the solution is cooled to an ambient temperaturefollowing a final injection of an additional amount of the Sn precursorsolution and the Te solution. In this embodiment, the final injectionmay occur at least 30 minutes following the initial mixing of the Snprecursor solution and the Te solution. In one embodiment, for example,the final injection of an additional amount of the Sn precursor solutionand the Te solution occurs at least 90 minutes following the initialmixing of the Sn precursor solution and the Te solution. By injectingthe Sn precursor solution and the Te solution over time, largernanomaterial may be grown to allow the absorption characteristics of thenanomaterial to be tuned to absorb longer IR wavelengths.

The injection of additional amounts of the Sn precursor solution and theTe solution also includes, in one example embodiment, injecting a lead(Pb) solution along with the additional amounts of the Sn precursorsolution and the Te solution at least one point in time. In oneembodiment, for example, the initial mixing of the Sn precursor solutionand the Te solution includes mixing the Sn precursor solution and the Tesolution along with a Pb solution. In this embodiment, the injection ofadditional amounts of Sn precursor solution and the Te solution may alsoinclude injecting the additional amounts of the Sn precursor solutionand the Te solution along with the Pb solution. By incorporating Pb intothe nanomaterials, the bandwidth that the resulting nanomaterial isconfigured to absorb may also be tuned so as to detect longerwavelengths of IR radiation.

The method of one embodiment may also maintain the solution at anelevated temperature for a dwell time such as a dwell time of at least15 minutes, following a final injection of the additional amounts of theSn precursor solution and the Te solution. In regards to maintaining themixture at an elevated temperature, the mixture may be maintained inaccordance with one embodiment at a temperature of at least 140° C.during and following the injection of an additional amount of the Snprecursor solution and the Te solution. The elevated temperature and theincorporation of a dwell time may also facilitate tuning the absorptioncharacteristics of the nanomaterial so as to detect longer IRwavelengths.

In accordance with another embodiment, a method of manufacturing a leadtin telluride (Pb_(x)Sn_(1-x)Te) nanomaterial includes introducing leadinto a container, such as by introducing a dried lead chloride solutioninto the container. The method of this embodiment also adds a tin (Sn)precursor solution and a telluride (Te) solution to the lead within thecontainer to form a solution and then maintains the solution at anelevated temperature for a period of time prior to cooling to an ambienttemperature to form the Pb_(x)Sn_(1-x)Te nanomaterial.

While adding the Sn precursor solution and the Te solution in accordancewith one embodiment, the lead is maintained at the first elevatedtemperature. In this embodiment, the solution may be maintained at asecond elevated temperature, less than the first elevated temperature,for a period of time after adding the Sn precursor solution and the Tesolution. In one embodiment, maintaining the solution at an elevatedtemperature includes maintaining the mixture at least 120° C. for theperiod of time after adding the Sn precursor solution and the Tesolution. In one embodiment, maintaining the solution at an elevatedtemperature includes maintaining the solution at an elevated temperaturefor at least 90 seconds prior to cooling to the ambient temperature toform the Pb_(x)Sn_(1-x)Te nanomaterial.

In accordance with embodiments of the quantum nanomaterials and themethod of manufacturing nanomaterial, quantum nanomaterials having abandgap that is tunable to permit detection of higher wavelengths of IRradiation including, for example, IR radiation throughout the MWIRregion and into the LWIR region, is provided. However, the features,functions and advantages that have been discussed may be achievedindependently in various embodiments of the present disclosure and maybe combined in yet other embodiments, further details of which may beseen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described embodiments of the present disclosure in generalterms, reference will now be made to the accompanying drawings, whichare not necessarily drawn to scale, and wherein:

FIG. 1 is a perspective view of a surface having a coating includingquantum nanomaterials in accordance with one embodiment to the presentdisclosure;

FIG. 2 is a flowchart illustrating operations performed in accordancewith a method of one embodiment of the present disclosure;

FIG. 3 is a graphical representations of the absorption spectrum of aSnTe nanomaterial manufactured with different numbers of repeatedinjections of additional amounts of an Sn precursor solution and a Tesolution in accordance with one embodiment to the present disclosure;

FIG. 4 is a graphical representation of the absorption spectrum of anundoped SnTe nanomaterial and a SnTe nanomaterial doped with Pb inaccordance with one example embodiment of the present disclosure;

FIG. 5 is a graphical representation of the x-ray diffraction (XRD)spectrum of a SnTe nanomaterial doped with Pb in accordance with oneexample embodiment to the present disclosure;

FIG. 6 is a flowchart illustrating the operations performed inaccordance with a method of another embodiment of the presentdisclosure;

FIG. 7 is a graphical representation of the absorption ofPb_(x)Sn_(1-x)Te nanomaterial manufactured in accordance with a processhaving different dwell times according to one example embodiment of thepresent disclosure;

FIG. 8 is a graphical representation of the absorption spectrum of aSnTe nanomaterial in comparison to a Pb_(x)Sn_(1-x)Te nanomaterialhaving different ratios of Pb to Sn in accordance with one exampleembodiment of the present disclosure;

FIG. 9 is a flowchart illustrating the operations performed inaccordance with a method of a further embodiment to the presentdisclosure;

FIG. 10 is a graphical representation of the absorption spectrum of anPb_(x)Sn_(1-x)Te nanomaterial having different ratios of Pb to Sn anddifferent dwell times in accordance with one embodiment to the presentdisclosure; and

FIG. 11 is a graphical representation of an XRD spectrum of a SnTenanomaterial doped with Pb in accordance with the embodiment of FIG. 8.

DETAILED DESCRIPTION

The present disclosure now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments are shown. Indeed, these embodiments may be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will satisfy applicable legal requirements. Likenumbers refer to like elements throughout.

A quantum nanomaterial and an associated manufacturing process aredisclosed according to embodiments of the present disclosure. Thequantum nanomaterials may be utilized for a variety of purposesincluding the absorption of IR radiation. As such, the quantumnanomaterials may be included within an optical detector, device orother sensor for detecting IR radiation or at least a predefinedbandwidth of the IR spectrum. Alternatively, the quantum nanomaterialmay be formed in a solution and may be incorporated into paints or othercoatings. In this regard, FIG. 1 illustrates a surface 10 and a coating12 deposited upon the surface. The coating 12 of this example embodimentincludes quantum nanomaterial that is responsive to a predefinedbandwidth of the IR spectrum. Thus, the coating 12 may effectivelyabsorb the predefined bandwidth of the IR spectrum as a result of theincorporation of the quantum nanomaterials therewithin.

The quantum nanomaterial may take the form of a quantum dot. Quantumdots form a potential well that confines carriers in three dimensionsand produce quantized, discrete energy states resembling those in anatom. Changing the size and shape of a quantum dot alters the spacing ofthe energy levels and therefore effects interactions between the quantumdot and incident radiation. For example, a decrease in quantum dot sizeincreases the quantum confinement and provides a smaller bandgap.Quantum dots may be synthesized utilizing a scalable solution synthesis.As part of the fabrication process, a surface and a shell or dopant ofanother material may be coated on or over the quantum dot to alter thelight interaction properties and to improve environmental stability.Since quantum dots are soluble in the solution, quantum dots may beprocessed into a coating 12 utilizing relatively low-cost solutionprocessing.

In accordance with an embodiment of the present disclosure, quantumnanomaterials may be fabricated such that the bandwidth of IR radiationto which the quantum nanomaterial is responsive may be advantageouslytuned, such as to bandwidths throughout the MWIR region and, in oneembodiment, into the LWIR region. In one embodiment, the quantumnanomaterial is formed of tin telluride (SnTe), while in anotherembodiment, the quantum nanomaterial is formed of lead tin telluride(Pb_(x)Sn_(1-x)Te) in which x has a value between 0.1 and 0.6.

In regards to a SnTe nanomaterial, the SnTe nanomaterial may bemanufactured as shown, for example, in FIG. 2. In this regard, a tin(Sn) precursor solution and a tellurium (Te) solution may be initiallymixed to form a solution. See operation 20 of FIG. 2. While the solutionis maintained at an elevated temperature, that is, at a temperaturegreater than ambient or room temperature, additional amounts of the Snprecursor solution and the Te solution may be injected into the solutionat a subsequent point in time. See operations 22-30 of FIG. 2. Followinga dwell time and cooling to an ambient temperature as shown in operation32, the solution may be processed to extract the SnTe nanomaterial. As aresult of the injection of additional amounts of the Sn precursorsolution and the Te solution as well as a result of the temperature atwhich the solution is maintained and the timing at which the injectionsof additional amounts of the Sn precursor solution and the Te solutionare mixed, the bandwidth within the IR spectrum that the resulting SnTenanomaterial is configured to absorb may be tuned including, forexample, to bandwidths within the MWIR region and into the LWIR region.

Although the SnTe nanomaterial may be formed in various manners, amethod of manufacturing the SnTe nanomaterial in accordance with oneembodiment is shown in FIG. 2. In this embodiment, a Sn precursorsolution and a Te solution are mixed at time 0 and at a predefined firstelevated temperature, such as 180° C. See operation 20. Once the Snprecursor solution and the Te solution have been mixed, the temperatureof the solution may be reduced to a second elevated temperature, such asto 140° C., and the initial solution may be held at this secondpredefined temperature for a first predetermined period of time, such as10 minutes. Thereafter, an additional amount of the Sn precursorsolution and the Te solution may be injected into the initial solution.See operation 22. The resulting solution may then be maintained at thesecond predetermined temperature for a second period of time, such as 20minutes. A plurality of additional injections of the Sn precursorsolution and the Te solution may then be introduced at different pointsin time to produce SnTe nanomaterial with a sufficiently broad bandgap,such as a bandgap between 0 eV and 0.35 eV. With reference to FIG. 2 byway of example, at 30 minutes following the initial mixing, anotheradditional amount of the Sn precursor solution and the Te solution maybe injected into the solution. See operation 24. As shown in FIG. 2,this repeated injection of an additional amount of the Sn precursorsolution and the Te solution may be done at several different points intime, such as at 45 minutes, 60 minutes and 90 minutes following theinitial mixing. See operation 30. In this regard, it is noted that thetime references in FIG. 2 and the other flowcharts are elapsed timesince the initial mixing. Following the final addition of the Snprecursor solution and the Te solution, the solution is maintained atthe second elevated temperature for a predefined dwell time, such as 30minutes, prior to allowing the solution to cool to room temperature. Seeoperation 32. The resulting solution may then be further processed inorder to obtain the SnTe nanomaterial.

In the illustrated embodiment, five additional injections of the Snprecursor solution and the Te solution are made following the initialsolution of the Sn precursor solution and the Te solution. However, anynumber of additional injections of the Sn precursor solution and the Tesolution may be made including four or fewer injections of additionalamounts of the Sn precursor solution and the Te solution including orsix or more injections of additional amounts of the Sn precursorsolution and the Te solution. Additionally, while the injections occurat time increments of 15 and 20 minutes in the above describedembodiment, other increments, such as between 5 and 30 minutes, may beestablished between injections in other embodiments. As will bedescribed below in conjunction with FIGS. 3 a and 3 b, the injection ofadditional amounts of the Sn precursor solution and the Te solutioncauses the wavelength at which the resulting SnTe nanomaterial has itspeak absorption to increase such as through the MWIR range and into theLWIR range in some embodiments.

The initial solution of the Sn precursor solution and the Te solution(operation 20) may be in the same proportion as all subsequentinjections of additional amounts of the Sn precursor solution and the Tesolution (operations 22-30). In one embodiment, however, the initialsolution of the Sn precursor solution and the Te solution has a greatervolume than any of the additional amounts of the Sn precursor solutionand the Te solution that are thereafter injected into the solution. Inthis regard, the method of one embodiment injects the same additionalamount of the Sn precursor solution and the Te solution at each of thedifferent points in time. For example, the additional amounts of the Snprecursor solution and the Te solution injected at operations 22-30 maybe between 40% and 60%, such as 50%, of the amounts of the Sn precursorsolution and the Te solution that were initially mixed at operation 20.However, other proportions of the Sn precursor solution and the Tesolution may be utilized in other embodiments.

In order to absorb longer wavelengths within the IR spectrum, the SnTenanomaterial may be advantageously manufactured so as to have largerparticles than those provided by conventional processes, such asnanocrystals having cross-sectional dimensions, such as diameters, of atleast 15 nm and, in some embodiments, up to at least 50 nm. In order togrow larger SnTe nanomaterials, the method of manufacturing inaccordance with one embodiment utilizes multiple injections ofadditional amounts of the Sn precursor solution and the Te solution overa longer period of time and, in one embodiment, at a higher temperature,such as exemplified by the embodiment of FIG. 2, than conventionaltechniques.

Although the method for manufacturing the SnTe nanomaterial may beperformed in a variety of different manners, one example embodiment ofthe method is described hereinafter for purposes of illustration, butnot of limitation. In this example method, a solvent, such as1-octadecene (ODE) having a purity of 90%, was vacuum dried at 140° C.for two hours and stored in an argon filled glove box withbis[bis(trimethylsilyl)amino] tin (II), trioctylphosphine (TOP) having apurity of at least 90% and Te powder having a purity of about 99.99%. At10 wt % solution of Te and TOP may then be prepared in a glove box bydissolving elemental Te in TOP at 200° C. for six hours. By utilizingTOP having a purity of about 90% as opposed to a higher purity, theresulting SnTe quantum dots were more monodispersed than if TOP having apurity of about 99% had been utilized.

A Sn precursor solution may then be formed in a glove box by dissolving0.48 mL (1.2 mmol) of bis[bis(trimethylsilyl)amino] tin (II) in 9 mL ofdry ODE and 9 mL of dry oleylamine (OLA) having a purity of about 70%.This solution may then be divided into 5 separate syringes containing 6mL, 3 mL, 3 mL, 3 mL and 3 mL (0.8 mmol Sn for the 6 mL syringe and 0.4mmol Sn for the 3 mL syringe). Additionally, 5 individual syringes maybe loaded with 1 mL, 0.5 mL, 0.5 mL, 0.5 mL and 0.5 mL of the Te in 90%TOP solution (0.73 mmol Te for the 1 mL syringe and 0.37 mmol Te for the0.5 mL syringe). Pairs of syringes containing the Sn precursor solutionand the Te solution were then sealed in 1 L Nalgene bottles to preventoxidation and removed from the glove box. As such, one Nalgene bottlecontains one syringe of 6 mL of the Sn precursor solution and onesyringe of 1 mL of the Te solution, while the other four bottles eachcontained one syringe of 3 mL of the Sn precursor solution and onesyringe of 0.5 mL of the Te solution.

In accordance with this embodiment, a three neck 100 mL flask with acondenser column and septa on the side necks may then be attached to avacuum/argon gas Schlenk line. 14 mL of an OLA solution may then beplaced in the flask and vacuum dried at 100° C. for one hour. The flaskmay then be backfilled with argon and the syringe with 1 mL of the Tesolution may then be injected. Once the reaction temperature is raisedto a first elevated temperature, such as between about 150° C. and 180°C., the syringe containing 6 mL of the Sn precursor solution may beremoved from the Nalgene bottle and injected into the flask whilerapidly stirring the mixture within the flask. This initial injectioninto the flask is considered to occur at time 0. The temperature of theflask may then be allowed to decrease to a second elevated temperature,such as by being allowed to drop by 30° C. to 40° C. following theinjection such that the reaction temperature is lowered to about 140° C.in one embodiment. As shown in operations 22, 24, 26 and 28 of FIG. 2,subsequent injections of the 3 mL Sn precursor solution and the 0.5 mLTe solution may be made at different points in time following theinitial injection, such as at 10 minutes, 30 minutes, 45 minutes and 60minutes following the initial injection. As shown at operation 30 inFIG. 2, an additional injection may be made at 90 minutes, however otherembodiments may have only four additional injections such that operation30 of FIG. 2 may be eliminated. Following the final injection, theresulting solution may be allowed to dwell for a dwell time, such as 30minutes, at the second elevated temperature, such as 140° C. Thereafter,the heat may be removed from the flask, such as by removing a heatingmantle that was previously heating the flask, and the solution may beallowed to cool to ambient temperature. See operation 32.

Thereafter, the SnTe nanomaterial may be precipitated. In oneembodiment, 3 mL of oleic acid (OA) may be injected into the flask andthen 10 mL of a 1:1 chloroform/acetone mixture may be added to the flaskfollowed by additional acetone to cause precipitation of the quantumnanomaterial. The resulting solution may be centrifuged to separate theSnTe nanocrystals and the supernatant may be poured off with the SnTenanocrystals being redissolved in chloroform. The precipitation,centrifugation and redissolution of the SnTe nanocrystals may beperformed a plurality of times, such as 3 times, to increase the purityof the resulting SnTe nanocrystals.

As shown in FIG. 3, the absorption spectrum of the resulting SnTenanomaterial varies based upon the wavelength of the incident IRradiation. In the embodiment described above and with additional amountsof the Sn precursor solution and the Te solution injected at 10 and 30minutes following the initial mixing as shown in operations 22 and 24 ofFIG. 2, the peak absorption of the absorption spectrum 36 of theresulting SnTe nanomaterial is about 3.7 μm as shown in FIG. 3. In thisregard, the increase in peak absorption with an additional injection isrepresented by FIG. 3 in which the peak absorption of 3.1 μm that isoccasioned by a single injection at 0 minutes (that is, during theinitial mixing) is shown by absorption spectrum 34 relative to the peakabsorption of 3.7 μm for absorption spectrum 36 that is attributable toinjections at both 10 and 30 minutes following the initial mixing.

The wavelength at which the resulting SnTe nanocrystal has a peakabsorption may be increased or shifted to the right relative to thegraphical representation of FIG. 3 by additional injection(s) of the Snprecursor solution and the Te solution into the solution over time, suchas at 45, 60 and 90 minutes following the initial mixing. See operations26, 28 and 30 of FIG. 2. In this instance, the absorption spectrum 42 ofthe resulting SnTe nanomaterial that was formed with five additionalinjections at 10, 30, 45, 60 and 90 minutes has a peak absorption of IRradiation having a wavelength of about 4.4 μm, greater than the peakabsorption of the absorption spectrums 34, 36 and 40 of the SnTenanomaterial that was formed with zero, two and four additionalinjections, respectively. As this example illustrates, additionalinjections of the Sn precursor solution and the Te solution over timemay further shift the wavelength at which the resulting SnTenanomaterial has peak absorption to even greater wavelengths, such asthrough the MWIR region and, in some embodiments, into the LWIR region.

As noted above, the increase in the wavelength at which the SnTenanomaterial has its peak absorption is based, at least in part, uponthe growth of larger SnTe nanoparticles. In order to allow the resultingSnTe nanoparticles to grow larger, the method of manufacture may includea growth period, e.g., a dwell period, following the final injection ofadditional amounts of the Sn precursor solution and the Te solution atan elevated temperature, such as the second elevated temperature. Inthis regard, the method of the example embodiment described abovemaintained the solution at the second elevated temperature of 140° C.for a dwell time of 30 minutes. However, the method of other embodimentsmay have a growth time of other lengths following the final injection ofan additional amount of the Sn precursor solution and the Te solution.In one embodiment, the growth time is greater than 10 minutes, such asat least 30 minutes in one embodiment which advantageously leads tored-shifted MWIR tunable nanomaterials that have a larger crystallinesize. During the growth time, the SnTe nanoparticles are allowed toOswald ripen into larger SnTe nanoparticles. However, the growth timeshould not be so long, such as greater than 120 minutes, so that thesize distribution of the larger SnTe nanoparticles is lost.

The absorption spectrum of the SnTe nanomaterial may also be modified bydoping the SnTe nanomaterial with lead (Pb). In this regard, doping theSnTe nanomaterial with Pb will also cause the wavelength at which theresulting nanomaterial has a peak absorption to increase, such as togreater wavelengths throughout the MWIR region or into the LWIR region.In order to absorb longer wavelengths within the IR spectrum, the PbSnTenanomaterial may be advantageously manufactured so as to have largerparticles than those provided by conventional processes, such asnanocrystals having cross-sectional dimensions, such as diameters, of atleast 7.5 nm. The SnTe nanomaterial may be doped with lead by eithergrowing the SnTe nanomaterial and then doping the resultingnanoparticles with Pb or by doping the SnTe nanomaterial with Pb duringthe growth of the nanomaterial. In an embodiment in which the SnTenanomaterial is first grown and then is subsequently doped with Pbfollowing its synthesis, the SnTe nanomaterial may be grown as describedabove. During the dwell time, however, concurrent with or following thefinal injection of an additional amount of the Sn precursor solution andthe Te solution, Pb may be added to the mixture, such as by injecting asolution of lead chloride (PbCl₂) into the solution and then maintainingthe solution at an elevated temperature, such as at the second elevatedtemperature of, for example, 140° C., for a period of time, such as 30minutes. In the example embodiment described above, a solution of 56 mgof PbCl₂ in OLA which results in a 1:4 mol ratio of Pb:Sn precursors maybe added to the solution with the solution then being held at the secondelevated temperature of 140° C. for at least 10 minutes. By maintainingthe solution at an elevated temperature for a period of time followingthe addition of the Pb, the Pb will partially anneal into the SnTematerial system so as to shift the absorption spectrum to a longerwavelength in a controlled manner. In this regard, FIG. 4 illustratesthe absorption spectrum 50 of an undoped SnTe material without Pb andthe absorption spectrum 52 of a corresponding SnTe material that isdoped with Pb. In this regard, FIG. 4 illustrates the absorptionspectrum of an undoped SnTe material without Pb and a corresponding SnTematerial that is doped with Pb. As will be seen, the peak absorption ofthe resulting SnTe nanomaterial is shifted from 4.2 micrometers for theundoped SnTe nanomaterial without Pb to 4.4 micrometers for the SnTenanomaterial that is doped with Pb. Furthermore, the x-ray diffractionspectrum of the SnTe material doped with Pb is shown in FIG. 5. Thepeaks designated by an asterisk (*) indicate reflections that match to aPb_(0.5)Sn_(0.5)Te reference pattern, and are indicative of theincorporation of Pb into the SnTe quantum dot, such as by partialsubstitution. The peaks designated by Q are indicative of reflectionfrom the quartz sample holder

In an alternative embodiment, Pb_(x)Sn_(1-x)Te nanomaterials may besynthesized via a partial substitution reaction in situ duringsynthesis. In this regard, Pb may be initially introduced into acontainer, such as a flask, and an Sn precursor solution and a Tesolution may be added to the Pb to form a solution. See operations 60and 62 of FIG. 6. The resulting solution may then be maintained at anelevated temperature for a period of time, e.g., a dwell time, prior tocooling the solution to an ambient temperature to form thePb_(x)Sn_(1-x)Te nanomaterial. See operation 64.

In one embodiment, OLA having a purity of about 70% may be vacuum-driedat 140° C. for two hours and then stored in an argon-filled glove boxalong with bis[bis(trimethylsilyl)amino] tin (II) top having a purity ofabout 90%, lead chloride having a purity of about 99.9%, and Te.Initially, the Sn precursor solution may be formed in a glove box bydissolving 0.16 ml (0.14 mmol) of bis[bis(trimethylsilyl)amino] tin (II)in 6 ml of dry ODE. This solution may be loaded into a 20 ml syringewith an 18 gauge needle. Additionally, 1 ml of Te in a TOP solution(0.73 mmol) may be loaded into a syringe. Both syringes may then besealed in a 1 L Nalgene bottle to prevent oxidation when the syringesare moved from the glove box.

A three neck 100 ml flask with a condenser column and septa on the sidenecks may be attached to a vacuum/argon gas Schlenk line. 14 mL of thesolution composed of OLA and 0.05-0.2 mmol of PbCl₂ may be placed in theflask and vacuum-dried at 100° C. for one hour, thereby havingintroduced lead into the flask as shown in operation 60 of FIG. 6. Theflask may then be back-filled with argon, and the temperature may beraised to a first elevated temperature, such as 180° C. The Sn precursorsyringe and the Te precursor syringe may then be removed from theNalgene bottle and injected into the flask while the contents of theflask are rapidly stirred. The temperature of the flask may then bereduced to a second elevated temperature, such as 120° C., followinginjection of the Sn precursor solution and the Te solution, and thesolution may then be maintained at the second elevated temperature for apredefined period of time (designated X in FIG. 6). For example, themixture may be maintained at the second elevated temperature for atleast 90 seconds, such as at least 11.5 minutes in one embodiment and atleast 40 minutes in another embodiment.

Following maintenance of the solution at the second elevated temperaturefor a predefined period of time, the solution may be allowed to cool toambient temperature, such as by removing the heating mantle that waspreviously heating the mixture. See operation 64. Thereafter, 3 ml of OAmay be injected followed by the addition of 10 ml of a 1:1chloroform/acetone mixture followed by the addition of additionalacetone to cause precipitation of the Pb_(x)Sn_(1-x)Te quantum dots. Thesolution may then be centrifuged to separate the Pb_(x)Sn_(1-x)Tenanocrystals and the supernatant may be poured off with the nanocrystalsthereafter being redissolved in chloroform. The precipitation,centrifugation and redissolution of the Pb_(x)Sn_(1-x)Te nanomaterialsmay be performed a plurality of times, such as three times, to increasethe purity of the resulting nanocrystals.

As noted above, the absorbance of a SnTe nanomaterial may be tuned byrepeatedly injecting additional amounts of the Sn precursor solution andthe Te solution over time and by the doping of the SnTe nanomaterialwith Pb. The absorbance may also be tuned by controlling the length ofthe dwell time with increased absorbance at higher wavelengthsattributable to the larger particle growth associated with longer dwelltimes, such as from 1 minute to 60 minutes. In this regard, FIG. 7provides a graphical representation of the absorbance of variouswavelengths within the IR spectrum of Pb_(x)Sn_(1-x)Te nanomaterialsthat were manufactured with dwell times of 1.5 minutes, 11.5 minutes and40 minutes (absorbance spectra 70, 72 and 74, respectively). As shown,the exciton peak of the Pb_(x)Sn_(1-x)Te nanomaterial may be shifted togreater wavelengths as the Pb_(x)Sn_(1-x)Te nanomaterial is manufacturedwith longer dwell times is annealed for longer periods of time. In thisregard, the exciton peak for Pb_(x)Sn_(1-x)Te nanomaterial that had adwell time of 1.5 minutes is at about 4.55 microns, the exciton peak forPb_(x)Sn_(1-x)Te nanomaterial that had a dwell time of 1.5 minutes is atabout 5.4 microns, and the exciton peak for Pb_(x)Sn_(1-x)Tenanomaterial that had a dwell time of 1.5 minutes is at about 5.9microns.

The exciton peak may also be repositioned by the absorbance spectrum 82for controllably varying the Pb content in a reaction solution, such asfrom a 1:2 Pb:Sn synthesis solution mole ratio to a 1:12 Pb:Sn synthesismole ratio or higher. As shown, for example in FIG. 8, the absorbancespectrum 82 for Pb_(x)Sn_(1-x)Te nanomaterial having a 1:8 Pb:Snsynthesis solution mole ratio has a shorter wavelength exciton peak thanthe absorbance spectrum 80 for Pb_(x)Sn_(1-x)Te nanomaterial made with a1:4 Pb:Sn synthesis solution mole ratio, e.g., 3.5 microns in comparisonto 4.55 microns. Additionally, the exciton peak of either type ofPb_(x)Sn_(1-x)Te nanomaterial has an exciton peak at a greaterwavelength than that of a comparable SnTe material having an absorbancespectrum 84 with an exciton peak at 3.15 microns.

As described above, the wavelength at which the peak absorption occursmay be increased by doping a SnTe nanomaterial with Pb either during theinitial introduction of the Sn precursor solution and the Te solutionare following the growth of the SnTe nanomaterial. However, even largerPb_(x)Sn_(1-x)Te nanomaterials may be fabricated by introducing Pb atone or more instances throughout the manufacturing process, such asconcurrent with a plurality of or each of the injections of additionalamounts of the Sn precursor solution and the Te solution, as well as, inone embodiment, along with the initial combination of the Sn precursorsolution and the Te solution. In some embodiments, a single additionalinjection of a Pb solution, the Sn precursor solution and the Tesolution may be sufficient to obtain Pb_(x)Sn_(1-x)Te nanomaterial witha bandgap that is wide enough to absorb IR signals in the MWIR regionand into the LWIR region. In other embodiments, however, the method mayinclude a plurality of injections of the Pb solution, the Sn precursorsolution and the Te solution at different points in time following theinitial mixing in order to obtain Pb_(x)Sn_(1-x)Te nanomaterial with asufficiently broad bandgap, such as a bandgap between 0 eV and 0.35 eV.Indeed, the plurality of injections of the Pb solution, the Sn precursorsolution and the Te solution at different points in time in accordancewith a method of one embodiment of the present invention cause a partialcation exchange of the Sn to Pb, as opposed to a total ion exchange,with the partial cation exchange leading to larger nanomaterials and, inturn, to a red shift of the band edge past the MWIR. In this regard,operation 90 of FIG. 9 illustrates a method in which the Sn precursorsolution and the Te solution are initially mixed along with a Pbsolution at time 0 and at a first elevated temperature, such as 180° C.In the illustrated embodiment, 0.8 mmol bis[bis(trimethylsilyl)amino]tin (II) and 0.73 mmol Te and 0.2 mmol PbCl₂ are mixed at a firstelevated temperature of 180°. The temperature of the mixture may then bereduced to a second elevated temperature, such as 140° C. The initialsolution may be held at the second elevated temperature for a predefinedperiod of time, such as ten minutes, prior to injecting additionalamounts of the Sn precursor solution, the Te solution and the Pbsolution, such as shown in operation 92 of FIG. 9. This process may berepeated at a plurality of different points in time, such as at 20minutes and 30 minutes following the initial mixing as shown atoperations 94 and 96, respectively. The final solution may then bemaintained at the second elevated temperature for a predefined dwelltime, such as 15 minutes in the illustrated embodiment. Thereafter, thesolution may be cooled to ambient temperature as shown at operation 98and the Pb_(x)Sn_(1-x)Te nanomaterial may then be precipitated,centrifuged and redissolved in a manner described above in order toextract the Pb_(x)Sn_(1-x)Te nanomaterials of a sufficient purity.

As shown in FIG. 10, a graphical representation of the absorptionspectrum 100 of a Pb_(x)Sn_(1-x)Te nanomaterial made in accordance withthe foregoing process of FIG. 9 to have an exciton peak of at least 8microns, such as at 8.8 microns, is provided. This absorption spectrum100 may be compared to the absorption spectrum 102 and 104 of thePb_(x)Sn_(1-x)Te nanomaterial made in a manner described in conjunctionwith FIG. 6 with a 1:8 Pb:Sn precursor ratio in regards to spectrum 102and a 1:4 Pb:Sn precursor ratio in regards to spectrum 104 and havingdwell times of 1.5 minutes and 11.5 minutes, respectively, and whichhave corresponding exciton peaks at 3.5 microns and 5.4 microns,respectively.

FIG. 11 provides the x-ray diffraction spectra of a SnTe nanomaterialthat has been doped with Pb injected at a plurality of different pointsin time, such as shown in FIG. 9. In FIG. 11, the peaks designated withan asterisk (*) indicate reflections that match to a Pb_(0.5)Sn_(0.5)Tereference pattern, and the peaks marked with a Q represent thereflections from the quartz sample holder. This x-ray diffraction datais indicative of the incorporation of Pb into the SnTe nanomaterial.Additionally, Scherrer broadening of the 23.2° 2θ diffraction peak givesan average crystallite size of 21.4 nm.

As described above, the band edge of the resulting SnTe nanomaterial maybe tuned to various wavelengths within the IR spectrum, includingthroughout the MWIR region and, in some embodiments, into the LWIRregion as a result of repeatedly injecting the feedstock at variouspoints in time and by controlling the timing and temperature of themanufacturing process. As such, SnTe nanomaterials may be manufacturedthat are capable of absorbing different or additional regions within theIR spectrum, thereby facilitating development of additional IR sensors,detectors, coatings 12 or the like for various applications.

Many modifications and other embodiments will come to mind to oneskilled in the art to which this disclosure pertains having the benefitof the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that thedisclosure is not to be limited to the specific embodiments describedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A method of manufacturing a tin telluride(SnTe) nanomaterial comprising the following steps in order: mixing atin (Sn) precursor solution and a tellurium (Te) solution to form amixed solution at a first elevated temperature; after the mixing,reducing a temperature of the mixed solution and then maintaining themixed solution at an elevated temperature, less than the first elevatedtemperature, for a period of time; after reducing the temperature of themixed solution at the elevated temperature for the period of time andwhile at an elevated temperature that is less than the first elevatedtemperature, repeatedly injecting additional amounts of the Sn precursorsolution and the Te solution into the mixed solution at different pointsin time; and maintaining the mixed solution at an elevated temperature,less than the first elevated temperature, for a period of time followingeach injection of an additional amount of the Sn precursor solution andthe Te solution into the mixed solution prior to a subsequent injectionof an additional amount of the Sn precursor solution and the Tesolution, wherein a resulting mixed solution is foamed following a finalinjection of an additional amount of the Sn precursor solution and theTe solution.
 2. A method according to claim 1 further comprising coolingthe resulting mixed solution to an ambient temperature following thefinal injection of the additional amount of the Sn precursor solutionand the Te solution which occurs at least 30 minutes following initiallymixing the Sn precursor solution and the Te solution.
 3. A methodaccording to claim 2 wherein the final injection of the additionalamount of the Sn precursor solution and the Te solution occurs at least90 minutes following initially mixing the Sn precursor solution and theTe solution.
 4. A method according to claim 1 wherein maintaining themixed solution at an elevated temperature for a period of time followingeach injection of an additional amount of the Sn precursor solution andthe Te solution comprises maintaining the mixed solution at atemperature of at least 140° C. during and following each injection ofan additional amount of the Sn precursor solution and the Te solution.5. A method according to claim 1 further comprising maintaining theresulting mixed solution at an elevated temperature for a dwell time ofat least 15 minutes following the final injection of the additionalamounts of the Sn precursor solution and the Te solution.
 6. A method ofmanufacturing a tin telluride (SnTe) nanomaterial comprising thefollowing steps in order: mixing a tin (Sn) precursor solution and atellurium (Te) solution to form a mixed solution; after the mixing,maintaining the mixed solution at an elevated temperature for a periodof time; after maintaining the mixed solution at the elevatedtemperature for the period of time, repeatedly injecting additionalamounts of the Sn precursor solution and the Te solution into the mixedsolution at different points in time, wherein repeatedly injectingadditional amounts of the Sn precursor solution and the Te solutionfurther comprises injecting the additional amounts of the Sn precursorsolution and the Te solution along with a lead (Pb) solution at at leastone of the points in time; and maintaining the mixed solution at anelevated temperature for a period of time following each injection of anadditional amount of the Sn precursor solution and the Te solution intothe mixed solution prior to a subsequent injection of an additionalamount of the Sn precursor solution and the Te solution, wherein aresulting mixed solution is formed following a final injection of anadditional amount of the Sn precursor solution and the Te solution.
 7. Amethod according to claim 6 wherein mixing the Sn precursor solution andthe Te solution comprises mixing the Sn precursor solution and the Tesolution along with a Pb solution, and wherein repeatedly injectingadditional amounts of the Sn precursor solution and the Te solutionfurther comprises injecting the additional amounts of the Sn precursorsolution and the Te solution along with the Pb solution at each of thedifferent points in time.
 8. A method according to claim 6 furthercomprising cooling the resulting mixed solution to an ambienttemperature following the final injection of the additional amount ofthe Sn precursor solution and the Te solution which occurs at least 30minutes following initially mixing the Sn precursor solution and the Tesolution.
 9. A method according to claim 8 wherein the final injectionof the additional amount of the Sn precursor solution and the Tesolution occurs at least 90 minutes following initially mixing the Snprecursor solution and the Te solution.
 10. A method according to claim6 wherein maintaining the mixed solution at an elevated temperature fora period of time following each injection of an additional amount of theSn precursor solution and the Te solution comprises maintaining themixed solution at a temperature of at least 140° C. during and followingeach injection of an additional amount of the Sn precursor solution andthe Te solution.
 11. A method according to claim 6 further comprisingmaintaining the resulting mixed solution at an elevated temperature fora dwell time of at least 15 minutes following the final injection of theadditional amounts of the Sn precursor solution and the Te solution.